Microinjection of foreign materials is often problematic, particularly if such microinjection is being performed on a biological structure such as a living cell. Various transfection techniques include the microinjection of foreign genetic material such as DNA into the nucleus of a cell to facilitate the expression of foreign DNA. For example, when a fertilized oocyte (egg) is transfected, cells arising from that oocyte will carry the foreign genetic material. Thus in one application organisms can be produced that exhibit additional, enhanced, or repressed genetic traits. As one example, researchers have used microinjections to create strains of mice that carry a foreign genetic construct causing macrophages to auto-fluoresce and undergo cell death when exposed to a certain drugs. Such transgenic mice have since played roles in investigations of macrophage activity during immune responses and macrophage activity during tumor growth.
Prior art microinjectors function in a similar manner to macro-scale syringes: a pressure differential forces a liquid through a needle and into the cell. In some cases a glass needle that has been fire drawn from a capillary tube can be used to pierce the cellular and nuclear membranes of an oocyte. Precise pumps then cause the expulsion of minute amounts of genetic material from the needle and into the nucleus.
Recently, researchers have produced fine microinjection needles from silicon nitride and silica glass that are smaller than fire drawn capillaries. These finer needles, however, still employ macro-scale pumps similar to those used in traditional microinjectors.